It has been known that a plurality of coating films having various functions are formed with layers on a surface of a base material such as a vehicle outer panel. These plurality of coating films simultaneously protect the base material and provide a high design property, thus, largely contribute to improve an appearance of an automobile, and resultantly to evoke buyer's willingness to buy the automobile.
Further, in recent years, as applications of the vehicle outer panel or the like, a multilayer coating film having a better feeling of depth is being developed. There is proposed a technology in which, for example, a metallic coating composition (A), a colored coating composition (B) and a clear coating composition (C) are sequentially coated, and a color difference ΔE between a multilayer coating film made of the metallic coating composition (A) and the clear coating composition (C) and a multilayer coating film made of the metallic coating composition (A), the colored coating composition (B) and the clear coating composition (C) is set within a predetermined range (see Patent Document 1). It is said that according to this technology, the better feeling of depth can be obtained since a metallic coating film of a lower layer can be visually seen through a colored coating film of an upper layer, and a color unevenness of the multilayer coating film can be prevented from occurring even when a film thickness of the colored coating film fluctuates slightly.
Further, there is proposed a technology in which a first coating composition containing a colored component and a photoluminescent material, a second coating composition containing a colored component and a clear coating composition are sequentially coated, and a content of the colored component in the second coating composition is set within an extremely small predetermined range relative to a resin solid content (see Patent Document 2). It is said that, according to this technology, a multilayer coating film having a better feeling of depth and high saturation can be obtained.
Further, there is proposed a technology in which a base coating composition (A) containing a photoluminescent pigment, a clear coating composition (B), a color clear coating composition (C) containing a colored pigment or a dye and a top clear coating composition (D) are sequentially coated, and each of a difference Δh of color phase angle h between a base coating film and a color clear coating film, a difference ΔL of brightness L* between the base coating film and a multilayer coating film and a difference ΔC of saturation C* between base coating film and the multilayer coating film is set within a predetermined range (see Patent Document 3). According to this technology, it is said that a color unevenness of a frame and the like generated in an edge part can be prevented from occurring, and a multilayer coating film having an excellent feeling of depth and high saturation can be obtained (see Patent Document 3).
Still further, there is proposed a technology in which in a method of forming a laminated coating film in which, after forming a first cured coating film by sequentially coating a first aqueous base coating composition containing a photoluminescent pigment and a first clear coating composition followed by baking and curing, a second cured coating film is formed by sequentially coating a second aqueous base coating composition which do not contain the photoluminescent pigment and a second clear coating composition, further followed by baking and curing, each of PWCs of the first aqueous base coating composition and the second aqueous base coating composition is set within a predetermined range, an L* value, a flip-flop value and a C* value of a first cured coating film are defined, and each of a second base coating film thickness, an L* value and a C* value is set within a predetermined range (see Patent Document 4). According to this technology, it is said that a color phase fluctuation due to a film thickness fluctuation can be suppressed, and a high saturation laminated coating film having excellent feeling of depth can be obtained.
Further, there is proposed a technology in which in a method of forming a multilayer coating film by sequentially coating a first aqueous base coating composition containing a photoluminescent pigment, a second aqueous base coating composition containing a colored pigment, and a clear coating composition, coating composition solid concentrations of the first aqueous base coating composition and the second aqueous base coating composition respectively are set within a predetermined range, a film thickness of the first base coating film is set within a predetermined range, and a film thickness ratio of the first base coating film and the second base coating film is set within a predetermined range (see Patent Document 5). It is said that, according to this technology, an orientation property of the photoluminescent pigment can be improved, and a multilayer coating film having a design property with high saturation and a better feeling of depth can be obtained (see Patent Document 5).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2000-279877
Patent Document 2: Japanese Patent No. 4455731
Patent Document 3: Japanese Patent No. 4886994
Patent Document 4: Japanese Patent No. 4822991
Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2011-147916